1. Field of the Invention
The present invention relates to an image forming apparatus utilizing an electron emitting device.
2. Related Background Art
A larger image size has been desired for image forming apparatuses such as CRT, and a thinner and lighter structure in such large image size is a target for such image forming apparatuses. As an image display apparatus capable of achieving such thinner and lighter structure, the present applicant has proposed an image display apparatus utilizing a surface conduction electron emitting device. Such image display apparatus utilizing the electron emitting device includes a vacuum container formed by sealing a rear plate, provided with plural electron emitting devices, and a face plate, provided with a light emitting member which emits light in response to an electron irradiation and an anode electrode, across a frame member in a peripheral portion.
In such image display apparatus utilizing electron emitting devices, as the luminance of display is proportional to an accelerating voltage, a high accelerating voltage has to be used in order to obtain a high display luminance. Also for realizing a thinner apparatus, a distance between the rear plate and the face plate has to be made smaller. Consequently, a considerably high electric field is generated between these plates, and may induce a discharge between the anode electrode receiving a high potential and other components.
Japanese Patent Application Laid-Open No. 2002-237268 (EP1220273A) discloses a configuration for avoiding a creepage discharge between the anode electrode and another component, by providing a guard electrode outside the anode electrode provided on the surface of the face plate and setting such guard electrode at a potential lower than that of the anode electrode.
In the Japanese Patent Application Laid-Open No. 2002-237268 (EP1220273A), the guard electrode described therein is provided in contact with a spacer for increasing the breakdown voltage, but a secure contact of the guard electrode with the spacer is not easy to achieve and is not favorable in consideration of the productivity. Also in case a small gap is formed between the electrode and the spacer because of an insufficient contact, there may result a discharge between the spacer and the electrode.